Characterization of a Salmonella Phage-Derived Endolysin LysSPYS2 and Its Combined Activity with Polymyxin B and Magnolol

Phage-derived endolysins are considered promising antibacterial agents for controlling bacterial pathogens. However, their activity against Gram-negative bacteria is usually limited by the outer membrane barrier. Salmonella enterica is a leading foodborne pathogen and an important target for endolysin-based control strategies. In this study, we identified and characterized LysSPYS2, an endolysin encoded by Salmonella phage SPYS_2. Recombinant LysSPYS2 was expressed in Escherichia coli Rosetta(DE3) and purified for activity assays. The optical density at 600 nm (OD600)-based turbidity-reduction activity, temperature and pH dependence under the tested conditions, and lytic spectrum of LysSPYS2 were determined using permeabilized bacterial suspensions. LysSPYS2 showed concentration-dependent turbidity reduction against Salmonella enterica serovar Typhimurium ATCC 14028, with the highest observed activity at 42 °C and pH 7. LysSPYS2 also showed lytic activity against several Gram-negative bacteria, with stronger activity against Salmonella strains. In intact-cell broth assays, LysSPYS2 alone showed limited growth suppression, whereas its growth-suppressive effect was enhanced when combined with polymyxin B or magnolol. These results suggest that LysSPYS2 may be further evaluated as a component of combination-based Salmonella control strategies.